Thanks to immense transmission capacity of the optical fiber, the wavelength divide multiplex (WDM) optical network is regarded as a mainstream technology for the next generation optical network having a huge transmission bandwidth. In the mean time, communication services, such as video conference, IPTV, distributed computing in data centers, are rapidly increasing and in particular for large scale data analysis in MapReduce, Hapdoop, and Spark with orientation towards stock prediction, disaster alarm, disease diagnosis, product recommendation, and user preference analysis. These business applications need to be carried out in one or multiple server clusters, with data transmission in a one-many or many-many communication mode, and bring immense transaction requirement for network support to high bandwidth multicast. With maturation in optical devices such as the semiconductor optical amplifier (SOA), optical coupler (OC), tunable optical filter (TOP), wavelength converter (WC), and arrayed waveguide grating (AWG), it is now an important research topic to design a multicast switching network based on optical devices to fully make use of the immense transmission capacity provided by the WDM optical network to satisfy ever-increasing multicast communication requirement.
The challenge in designing a multicast optical switching network is to realize the system scalability and non-blocking requirement while taking into account the following considerations:
(1) with an ever increasing network, the number of the active optical devices should not increase too rapidly, as these active optical devices monopolize equipment cost and energy consumption in the system;
(2) the scale of passive optical devices should not be too big, as the performance of the passive optical devices, such as AWG and OC, drastically deteriorate with the increase in the number of input and output ports;
(3) the number of wavelengths, as one of the important resources adopted in the system, should also not be too big; and
(4) the complexity of the algorithm used by the multicast switching network should be as low as possible, so that the algorithm may be easily implemented in the system.
To meet the above challenges, five design schemes for the AWG based multicast optical switching network are carried out currently:
The first scheme consists of an SOA based non-blocking crossbar network from SOA optical switches. A 1×N OC corresponds to each input port, and an N×1 OC corresponds to each output port, with each 1×N OC output port being connected with each N×1 OC input port via an SOA. The number of the SOAs required by the N×N switching network is O(N2), and hence the scheme is poorly scalable.
The second scheme is to construct a sparse crossbar network for realizing switching functions. The number of the SOAs in the second scheme is less than that of the first scheme, but the number of the SOAs is still in the order of O(N2) for an N×N switching network.
The third scheme is to construct a switching network in three stages via an SOA-based crossbar network modules, with each stage comprising multiple smaller scale SOA switching matrix modules and each module being connected with each module in a neighboring stage. Such a scheme decreases the number of employed SOAs but requires a non-blocking routing algorithm with a complexity of O(dN) for an N×N network. In the mean time, links in each stage do not fully take the advantages offered by WDM networks, and instead, with each link carrying a wavelength, and therefore the internal complexity of the network is relatively high.
The fourth scheme is to construct a switching network in two stages via AWG-based switching modules and SOA-based switching matrix. On one hand, such a scheme does not provide a feasible non-blocking routing algorithm; on the other hand, the SOA based switching matrix does not take consideration of wavelength divide multiplex properties, and thus the internal complexity of the network is also relatively high.
The fifth scheme is to construct a multicast non-blocking switching network based on an AWG. Such a scheme employs part of the input ports of the AWG as unicast input ports, with the remaining ones as multicast input ports. Data of a multicast request need an extra switching for multicast entrance to the network, and thus the multicast capacity is limited in addition to an extra switching. Moreover, the numbers of the input and output ports of the AWGs, the tuning scope of the wavelength converter, and the wavelength granularity of the system all increase with the increase of the scale of the network, resulting in poor scalability of the system.